Phloroglucinol developer for lingt-sensitive planographic plates

ABSTRACT

Planographic printing plates sensitized with a benzene diazonium salt are converted into offset printing forms by imagewise exposure and subsequent development with an aqueous phloroglucinol solution buffered to a pH between 4 and 8 and containing 1-10 percent by volume of water-miscible organic solvent having a molecular weight greater than 50. The organic solvent avoids or greatly reduces a problem of initial prints being blemished by ink held on blank (background) areas of the printing forms. Especially effective solvents, such as propyl glycol, acetonyl acetone, diacetone alcohol, and Nmethylpyrrolidone-2, having boiling points above 90* C. A high salt content in the developing solution inhibits any bleeding of the azo-dyestuff during development.

United States Patent Aloysius Henricus Jacobus Hllhorst Helden;

Paul Joseph Hubert Tummers, Velden, both of Netherlands Jan. 9, 1969 Sept. 21 1971 Van Der Grinten N. V.

Venlo, Netherlands Jan. 12, 1968 Netherlands Inventors Appl. No. Filed Patented Assignee Priority US. Cl 96/33, 96/49 G031 7/02 Int. Cl Field of Search References Cited UNITED STATES PATENTS Primary Examiner-Norman G. Torchin Assistant Examiner-John Winkelman Attorneys-Albert C. Johnston, Robert E. lsner, Lewis H.

Eslinger and Alvin Sinderbrand ABSTRACT: Planographic printing plates sensitized with a benzene diazonium salt are converted into offset printing forms by imagewise exposure and subsequent development with an aqueous phloroglucinol solution buffered to a pH between 4 and 8 and containing l-lO percent by volume of water-miscible organic solvent having a molecular weight greater than 50. The organic solvent avoids or greatly reduces a problem of initial prints being blemished by ink held on blank (background) areas of the printing forms. Especially effective solvents, such as propyl glycol, acetonyl acetone, diacetone alcohol, and N-methylpyrrolidone-2, having boiling points above 90C. A high salt content in the developing solution inhibits any bleeding of the azo-dyestuff during development.

PHLOROGLUCINOLY DEVELOPER FOR LIGHT-SENSITIVE PLANOGRAPP'IIC PLATES This invention relates to a developing process and a developing composition for the production of printing forms having oleophilic azo-dyestufi images thereon by the treatment of light-sensitive planographic plates after image-wise exposure of planographic surfaces thereof sensitized with a light-sensitive benzene diazonium compound.

British Pat. specification Nos. 1,038,279 and 1,082,889 describe a process for the production of printing forms in which a paper planographic plate sensitized with an activecoupling benzene diazonium salt is imagewise exposed and subsequently developed by means of an aqueous, buffered phloroglucinol solution having a slightly acid or neutral reaction. From a printing form thus obtained some hundreds of prints can be produced.

British Pat. Specification No. 1,064,128 describes a similar process in which a photographic barayta paper sensitized with a light-sensitive benzene diazonium slat is image-wise exposed and subsequently developed by means of an aqueous, buffered alkaline phloroglucinol solution. The use of alkaline phloroglucinol developers is, however, not desirable, because in solutions having a pH greater than 8.5 phloroglucinol has little resistance to deterioration caused by the oxygen prevailing in the air.

In German Pat. Specification No. 857,888 a process is described in which an anodically oxidized aluminum plate sensitized with a relatively slow-coupling benzene diazonium salt if imagewise exposed and subsequently developed by means of a solution of an azo-coupling component which preferably is a p'olyvalent aromatic hydroxyl compound, such as 2,4,2,4 tetrahydroxyldiphenyl.

Printing forms can be produced in a simple and inexpensive way according to the processes described in said British Pat.

Specifications Nos. 1,038,279, 1,082,889 and 1,064,128. These processes are preferably carried out by applying a weakly acid to neutral buffered phloroglucinol solution to a light-sensitive planographic plate on which an active-coupling diazo compound is present. The planographic plate to be sensitized can be an aluminum or a plastic foil having a planographic surface, or a so-called paper planographic printing plate.

On the other hand, quite a lot of the active-coupling benzene diazonium compounds useful for sensitizing the lightsensitive planographic plates according to the above-mentioned processes have a photochemical decomposition product which is more or less oleophilic, so that when the developed plates are used for printing the blank or highly exposed background areas of the images formed on them tend to hold small amounts of ink and produce a printing tone. This toning manifests itself on the first prints but gradually disappears as the printing process proceeds.

This phenomenon of initial toning occurs especially when the development of the planographic printing forms is effected in a cold and dry atmosphere. The initial toning is particularly annoying if only a small number of prints (50-200) are made from the printing form, for the first 20 or 30 prints are often unusable.

Another difficulty often encountered in the above-mentioned processes is that the azo-dyestuff image shows poor adherence to the planographic layer and, moreover, takes up the printing ink in sufficiently at the start of printing.

It has now been found that the above disadvantages can be avoided or made to occur to a far lesser extent in a process of the nature above mentioned, in which an imagewise exposed light-sensitive planographic surface sensitized with a light-sensitive benzene diazonium compound is developed into an oleophilic azo-dyestuff image by means of an aqueous, buffered phloroglucinol solution having a pH between 4 and 8, if to the phloroglucinol solution there is added l-l percent and preferably 3-6 percent by volume of an organic solvent that is at least percent by volume miscible with water and has a molecular weight of more than 50.

Any of various organic solvents of that nature can be used effectively according to the invention. Examples of suitable solvents are: aliphatic monovalent alcohols having at least three carbon atoms in the molecule, such as n-propanol; isopropanol or tertiary butanol; ethylene glycol monoalkyl ethers, such as methyl glycol or n-propylglycoli di or triethylene glycol monoand dialkyl ethers, such as diethylene glycol monomethyl-, monoethyl-, mono-n-propyl or mono-m butylethe'r, diethylene glycol dimethylor diethyl ether oi triethylene glycol dimethyl ether; esters of ethylene glycol diethylene glycoland triethylene glycol monoalkyl enters, such as methyl glycol formate, inetliyl glycol acetate, ethyl glycol acetate, diethylene glycol monomethyl ether forma'te or diethylene glycol monomethyl ether acetate; esters of 'formie acid or acetic acid and aliphatic monoor polyvalent alcohols, such as methyl formate, ethyl formate, glycerol monoacetate, glycerol 1,2-diacetate or glycerol 1,3 diacetate; aliphatic ketones, such as acetone, methyl ethyl ketone or a'cetoriyl acetone; keto alcohols such as diacetone alcohol; and hetero= cyclic solvents lacking pronounced aromatic properties, Such as dioxane and N-methyl pyrrolidone-2.

Preferably a nontoxic, inodorous solvent is chosen which at room temperature has a rate of evaporation approximately equaling that of water. The advantage of using such a solvent is in that the ratio between water and solvent does not chahge when the developer is stored in open vessels, for instance in ari open bottle or in the trough of a thin layer developing ap-' paratus such as widely used in the diazo-type process.

For this reason, solvents having a boiling point above C. are preferably chosen; and n-propyl glycol, acetoriyl acetone,

diacetone alcohol and N-mcthylpyrrolidone -2 have proved to be particularly effective.

The addition of an organic solvent according to the invention has not only the advantage that the initial toning is coun teracted but also that a better adherence of the image and good spreading of the developer over the planographic plates to be developed are obtained. Ergo, it is not necessary to add a wetting agent to the developer.

The developer is buffered at a pH between 4 and 8 and preferably between 6 and 7.5. The developer can contain as buffer salts the salts commonly used for buffering neutral to weakly acid phloroglucinol developers, such as ammonium, alkali metal or alkaline earth metal salts of weak acids such as phosphoric acid, acetic acid, adipic acid, maleic acid, tartaric acid and citric acid.

It is generally desirable to use a developer having a relative-' 1y high salt content, as in this way any bleeding of the alcdyestuff during development is reduced to a mihirnum and azo-dyestuff images having sharp contours are obtained.

In a particular embodiment of the invention the phloroglucinol solution, in order to prevent any bleeding of the azodyestuff during its development, is made to contain, in addition to the buffer salt, l-10 percent by weight of a water-soluble inorganic salt derived from a strong acid, such as sodium chloride, sodium bromide, sodium iodide, sodium sulfate, sodium nitrate, potassium chloride, potassium bromide, potassium iodide, potassium nitrate, potassium sulfate, ammonium bromide, ammonium nitrate, ammonium sulfate, lithium sulfate, calcium chloride, magnesium chloride, magnesium nitrate, magnesium sulfate or aluminum sulfate,

It goes without saying that the salt and the quantity thereof to be added to the developer must be selected in such away that no precipitates are formed in the developer. It is evident for instance, that no calcium, aluminum or magnesium salt should be added to a developer containing a phosphate as buffer salt.

Besides phloroglucinol the developer can contain other azocoupling components. In addition, auxiliary agents may be added, for instance, a reducing agent such as thiourea and a stabilizer such as hydroquinone monosulfonic acid.

The processes described in the examples below for the conversion of light-sensitive planographic plates into printing forms by exposure and development were carried out in a room at a constant temperature of 18 C. and a constant relative'humidity of 57 percent, and all the developers had a temperature of 18 C.

In the examples four planographic plates A, B, C and D were used. These planographic plates were obtained by sensitizing a planographic layer made according to disclosures of a copending application, Ser. No. 790,174, filed Jan. 9, 1969, which layer was previously formed on a highly glazed paper of 100 g/m in weight by the application of a dispersion containmg:

500 ml. of an aqueous solution containing 66 g. per liter of polyvinyl alcohol having a degree of hydrolysis of 99.8 percent,

220 ml. of an aqueous dispersion containing per liter 730 g.

of titanium dioxide doped with silicon dioxide and aluminum oxide and having an average particle size of about 0.2 u,

1 ml. of waterglass,

81 ml. of a 40 percent solution of glyoxal in water,

55 ml. of isopropanol, and water to bring the volume of the dispersion up to 1,000 ml.

The coating layer was dried and hardened by heating for to 20 seconds at 155 to 160 C., its weight amounted to about 12 g./m.

Plate A was sensitized with a solution containing:

27 g. of 4-(4'-methoxyphenylthio) S-methoxy Z-N-ethoxycarbonyl N-methylamino benzene diazonium chloride, zinc chloride double salt,

8.3 g. of boric acid,

1.7 g. of tartaric acid,

400 ml. of isopropanol, and

600 ml. of water.

The sensitized plate contained about 0.5 millimole of diazonium salt per m Plate B was sensitized with a solution containing:

20 g. of 4-benzoyl amino 2,5-di-n-butoxy benzene diazonium chloride, zinc chloride double salt,

8.4 g. of boric acid,

1.6 g. of tartaric acid,

300 ml. of isopropanol, and

700 ml. of water.

The sensitized plate contained about 0.5 millimole of diazonium salt per m3.

Plate C was sensitized with a solution containing:

13 g. of 4-dimethylamino 2-(440 -methylphenylthio) 3- chlorobenzene diazonium chloride, zinc chloride double salt,

8.4 g. of boric acid,

1.6 g. of tartaric acid,

300 ml. of isopropanol, and

700 mlfof water. The sensitized plate contained about 0.5

millimols of diazonium salt per m.

Plate D was sensitized with a solution containing:

20 g. of 4-bis (2'-acetoxyethyl) amino 3-(2, 4, 5-

trichlorophenoxy) fi-chlorobenzene diazonium chloride, zinc chloride double salt,

8.4 g. ofboric acid,

1.6 g. of tartaric acid,

300 ml. 'of isopropanol, and I 700 ml. of water.

The sensitized plate contained about 0.5 millimole of diazonium saltper m.

EXAMPLE I A presensitized plate A was imagewise exposed under a typewritten text on transparent material having a good density for the copying light, until the diazonium compound under the image-free areas of the original had been bleached out. The exposed plate was cut longitudinally into halves and the strips were marked Al and A2.

In a known type developing apparatus for thin-layer development, equipped with a smooth metal liquid-application roller, strip Al was developed 'with a developer of the following composition: i l i 7.5 g. of phloroglucinol,

5 g. of thiourea,

l g. of hydroquinone monosulfonic acid, potassium salt,

70 g. of disodium phosphate (2 aq),

60 g. of sodium sulfate and 40 ml. of n-propylglycol, in demineralized water up to a volume of 1,000 ml. The pH of this developer was about 8.

Strip A2 was developed with a similar developer from which, however, the n-propylglycol had been omitted. immediately upon development the two strips were clamped side by side onto the plate cylinder of an ofiset printing machine, and 200 prints were made. I

The first copies of strip Al showed no initial toning, whereas those of strip A2 showed an intensive initial toning. Analogous results are obtained when strip A1 is developed with a developer of one of the compositions described below and strip A2 with the corresponding developer without any organic solvent:

a. 10 g. of phloroglucinol,

2.5 g. ofthiourea, 1 g. of hydroquinone monosulfonic acid, potassium salt, 45 g. of dipotassium maleinate, 5 g. of maleic acid, g. of ammonium chloride, and 60 ml. of glycerol monoacetate, dissolved in demineralized water up to 1,000 ml.; pH about 5.5. b. 9 g. ofphloroglucinol,

4 g. of thiourea, 0.8 g. of hydroquinone monosulfonic acid, potassium salt, 60 g. of trisodium tartrate, 3 g. of tartaric acid, 75 g. of ammonium sulfate, and ml. of n-propanol, in demineralized water up to 1,000

ml.; pH about 5. Instead of 100 ml. of n-propanol it is possible, without affecting the result obtained with it, to add 50 ml. of ethyl formate or 100 ml. of dioxane to the last-described developer.

EXAMPLE [I A presensitized plate B was imagewise exposed until the diazonium compound under the image-free areas of the original had been bleached out, and was subsequently cut longitudinally into halves. The strips were marked B1 and B2.

In the way described in example I, strip B1 was developed with a developer of the following composition:

8 g. of phloroglucinol, 4 g; of thiourea,

l g. of hydroquinone monosulfonic acid, potassium salt,

50 g. of trisodium citrate (2 aq),

'100 g. of sodium chloride,

2 g. of citric acid and 60 ml. of n-propylglycol, in demineralized water up to 1,000

ml. The pH of this developer was about 5.5. Strip B2 was developed with a corresponding developer without n-propylglycol.

The two strips were clamped side by side on the plate cylinder of an offset printing machine, and the machine was then operated to make prints of them. From strip Bl over good prints were made, from strip B2 not a single good print was obtained. At the start of printing strip B2 took up ink over the whole of its surface, and it showed strong image wear. On the other, hand, the first few prints from strip Bl showed only a slight initial toning.

EXAMPLE III A presensitized plate C was imagewise exposed as described in example I, and subsequently cut longitudinally into halves to form strips which were marked C1 and C2.

Strip C1 was developed with the n-propylglycol-containing developer of example II and strip C2 with the corresponding developer without n-propylglycol. The developers were applied to the strips with a tampon.

The developed strips were clamped and run side by side on the plate cylinder of an offset printing machine. From strip C1 over 100 good prints were made; from strip C2 no good prints could be obtained, owing to the fact that an intensive initial toning and rapid image wear occurred.

EXAMPLE IV Strip D2 was developed with a corresponding developerwithout n-propylglycol.

The developers were applied to the strips with a tampon. The developed strips were clamped side by side on the plate cylinder of an offset printing machine and 250 prints were made. The first few prints of strip D2 showed much more initial toning than those of strip D1. Moreover, the image on strip D2 appeared to wear off more quickly.

EXAMPLE V A presensitized plate A was imagewise exposed until the diazonium compound under the imagefree areas of the original had bleached out, and was subsequently developed with a developer of the following composition:

g. of phloroglucinol,

3 g. of thiourea,

0.8 g. of hydroquinone monosulfonic acid, potassium salt,

80 g. ofdisodium phosphate (2 aq),

14 g. ofcitric acid,

70 g. of potassium iodide and 20 ml. of diethylene glycol dimethyl ether, in water up to l ,000 ml. The pH of this developer was about 6.

Development was effected with the aid of a tampon pad soaked in the developer. The developed plate was mounted on the offset printing machine and finally washed with water. From the plate at least 200 good prints were obtained. The first copies had no initial toning. When, on the other hand, use was made of a corresponding developer which did not contain diethylene glycol dimethyl ether, the first few prints showed distinct initial toning.

instead of the above-described developer composition, one of the developers described below may also be used to like advantage:

a. 6 g. ofphloroglucinol,

4 g. of thiourea, 0.5 g. of hydroquinone monosulfonic acid, potassium salt, 40 g. of disodium adipate, 0.5 g. of adipic acid, 60 g. of magnesium sulfate and 60 ml. of methylethyl ketone, in water up to 1,000 ml.,

pH is about 6.2. 9 g. ofphloroglucinol,

6 g. ofthiourea, l g. of hydroquinone monosulfonic acid, potassium salt, 80 g. of trisodium citrate (2 aq), l g. of citric acid, 80 g. of potassium chloride and 30 ml. of diacetone alcohol, in water up to 1,000 ml.; pH

is about 6.52. Instead of 30 ml. of diacetone alcohol 30 ml. of acetonyl acetone can be used the last-described developer without any difficulties being involved.

EXAMPLE VI A presensitized plate A was imagewise exposed as described in example I and developed with a developer of the following composition:

7 g. of phloroglucinol,

4 g. of thiourea,

1 g. of hydroquinone monosulfonic acid, potassium salt,

120 g. of sodium acetate,

100 g. of sodium chloride and 50 g. of methylglycol acetate, in water up to 1,000 ml. The

pH of this developer was about 7. The developed plate was clamped on the plate cylinder of the offset printing machine and finally washed with water. More than 200 good prints were obtained. The first few prints had no initial toning.

When the plate was developed with a corresponding developer without methylglycol acetate, the first few prints showed an intensive initial toning.

Instead of the developer described above, a developer of the following composition can also be applied with the same result:

12 g. of phloroglucinol,

6 g. of thiourea,

l g. of hydroquinone monosulfonic acid potassium salt,

25 g. of monosodium citrate (l aq),

31.4 g. oftrisodium citrate (5 aq),

100 g. of ammonium bromide and 25 ml. of N-methylpyrrolidone-Z, in water up to 1,000 ml.;

pH is about 4.3.

It is to be understood that the invention herein disclosed and defined by the appended claims may be carried out in ways other than those particularly mentioned above or illustrated by the examples. The invention is not intended to be limited by particulars of the foregoing description or examples except as may be required for fair interpretation of the claims.

What is claimed is:

1. In a process for the production of printing forms in which a light-sensitive planographic printing plate having a pianographic surface sensitized with a light-sensitive benzene diazonium compound is imagewise exposed and thereafter is developed, so as to form an oleophilic azo-dyestuff image, by applying to said surface an aqueous buffered phloroglucinol solution having a pH between 4 and 8, the improvement wherein said phloroglucinol developer solution contains l-l0 percent by volume of organic solvent that is at least 10 percent by volume miscible with water and has a molecular weight greater than 50.

2. A process according to claim 1, wherein said solvent is one also having a boiling point above C.

3. A process according to claim 1, said solvent being selected from the group consisting of n-propylgylcol, acetonyl acetone, diacetone alcohol and N-methylpyrrolidone-Z.

4. A process according to claim 1, further characterized in that said solution contains as buffering salt at least one alkaline-reacting salt of weak acid and in addition contains ll 0 percent by weight of at least one water-soluble inorganic salt of a strong acid, which salts do not react together to form a precipitate in said solution.

5. A composition for developing into an oleophilic azodyestuff image an imagewise exposed, light-sensitive planographic printing surface sensitized with a benzene diazonium compound, comprising an aqueous solution of phloroglucinol containing buffering salt giving the solution a pH between 4 and 8 and containing l-l0 percent by volume of water-miscible organic solvent selected from the group consisting of npropylglycol, acetonyl acetone, diacetone alcohol and N- methylpyrrolidone-2.

' 6. A composition according to claim 5, said buffering salt comprising at least one alkaline-reacting salt of a weak acid,

said solution also containing l-lO percent by weight of at least one waterosoluble inorganic salt of a strong acid, which salts do not react together to form a precipitate in said solution. 

50. THE ORGANIC SOLVENT AVOIDS OR GREATLY REDUCES A PROBLEM OF INITIAL PRINTS BEING BLEMISHED BY INK HELD ON BLANK (BACKGROUND) AREAS OF THE PRINTING FORMS. ESPECIALLY EFFECTIVE SOLVENTS, SUCH AS PROPYL GLYCOL, ACETONYL ACETONE, DIACETONE ALCOHOL, AND N-METHYLPYRROLIDONE-2, HAVING BOILING POINTS ABOVE 90*C. A HIGH SALT CONTENT IN THE DEVELOPING SOLUTION INHIBITS ANY BLEEDING OF THE AZO-DYESTUFF DURING DEVELOPMENT.
 2. A process according to claim 1, wherein said solvent is one also having a boiling point above 90* C.
 3. A process according to claim 1, said solvent being selected from the group consisting of n-propylgylcol, acetonyl acetone, diacetone alcohol and N-methylpyrrolidone-2.
 4. A process according to claim 1, further characterized in that said solution contains as buffering salt at least one alkaline-reacting salt of weak acid and in addition contains 1-10 percent by weight of at least one water-soluble inorganic salt of a strong acid, which salts do not react together to form a precipitate in said solution.
 5. A composition for developing into an oleophilic azo-dyestuff image an imagewise exposed, light-sensitive planographic printing surface sensitized with a benzene diazoniUm compound, comprising an aqueous solution of phloroglucinol containing buffering salt giving the solution a pH between 4 and 8 and containing 1-10 percent by volume of water-miscible organic solvent selected from the group consisting of n-propylglycol, acetonyl acetone, diacetone alcohol and N-methylpyrrolidone-2.
 6. A composition according to claim 5, said buffering salt comprising at least one alkaline-reacting salt of a weak acid, said solution also containing 1-10 percent by weight of at least one water-soluble inorganic salt of a strong acid, which salts do not react together to form a precipitate in said solution. 